Ultrahigh-frequency broadcast antenna system



3 Sheets-Sheet Nov. 3, 1953 o. o. Flr-:T ETAL ULTRAIIIGH-FREQUENCY BROADCAST ANTENNA vSYSTEM Filed March 1e, lesa Nov. 3, 1953 o. o. Flr-:T ETAL ULTRAHIGH-FREQUENCY BROADCAST ANTENNA SYSTEM 3 Sheets-Sheet 2 Filed March 16, 1950 ATTORNEY Nov. 3, 1953 ULTRAHIGH-FREQUENCY BROADCAST ANTENNA SYSTEM Filed March 16, 1950 3 Sheets-Sheet 3 had* ATTORNEY Patented Nov. 3, 195g ULTRAHIGH-FREQUENCY BROADCAST ANTENNA SYSTEM Owen Orlando Fiet, Oaklyn, and Robert Marion Seudder, Westmont, N. J., assignors to Radio Corporation of America, a corporation of Dela- War@ Application March 16, 1950, Serial N o. 150,078

(Cl. Z50-33) 11 Claims.

This invention relates to antennas and it particularly pertains to ultra-high frequency slot radiator arrays and transmission line assemblies therefor.

Broadcasting of radio and television programs in the frequency band lying between 500 and 890 megacycles has imposed stringent requirements for the necessary antenna systems. Effective powers of 10 to 20 kilowatts are desirable. The bandwidth requirement is no less serious than for similar lower frequency services. The effect of deiiection of the antenna and the supporting tower in high winds must not seriously affect `the signal strength at any receiver located within the intended service area. Antenna power gains of the order of 20 to 25 times that obtained with a simple dipole tuned to the frequency of measurement are likewise desirable.

Another factor to be considered in the ultrahigh frequency bands is that the dimensions of the radiation system being much smaller, there is less than sumcient room for the prior art type of transmission line assemblies.

It is an object of the invention to provide an ultra-high frequency, omnidirectional, high power antenna system of simple construction for operation over a relatively wide frequency band.

It is another object of the invention to provide a slotted antenna system in which beam tilting with frequency change is reduced or eliminated.

It is a further object of the invention to provide a slotted antenna system in which energy in the TEM mode is utilized and effects of TE1,1 and other non-cylindrical modes are suppressed.

It is still another object of the invention to provide means to obtain maximum efciency from each of the several layers of a multi-layer slotted antenna.

It is yet another object to provide a slot antenna constructed in accordance with the foregoing objects having a simple, single-element centrally-located transmission line.

These and other objects of the invention which will appear as the specification progresses are attained by means of a transmitting or receiving antenna system comprising a hollow tubular conductive member having a plurality of elongated longitudinal slots arranged along the length thereof in groups or layers of slots spaced about the periphery. Each of the slots is coupled to the interior of the conductive member by means of an adjustable probe member attached to the hollow tubular conductive member at an edge of each slot. Additional probe members placed between layers of slots may be used advantageously to vary the impedance of the network between the layers of slots to match the respective slots to the portions of the transmis- Sion line to which they are coupled. Wave energy is introduced into the interior of said member in the transmission line or TEM mode by means of a centrally-located conductor assembly having an interruption at or near the center thereof effecting two lengths of coaxial transmission line in conjunction with the slotted radiator or receptor member. The ends of the hollow conductive member may be electrically connected to the centrally-located conductor, and if so, the means for such connections also preferably serve as a means of mechanical support. Preferably at least a part of the centrally-located conductor is hollow from the point of interruption to one end and contains a further conductor thus forming a further section of coaxial transmission line to which a transducer is coupled. Preferably the transducer is coupled to the last-mentioned transmission line by means of a waveguide though it may be coupled directly with only small loss in efciency.

The invention will be described with reference to the accompanying drawing forming a Dart of the specication and in which:

Fig. 1 is an elevation view of an antenna system according to the invention;

Fig. 2 is an enlarged cross-section view of a portion of the antenna shown in Fig. 1 illustrating essential details of an antenna system according to the invention;

Fig. 3 is an end View of the radiator of the antenna according to the invention;

Figs. 4-6 are cross-section views of the arrangement of Fig. 2 taken along lines ll-, 5 5, and 8 6;

Fig. '7 is a schematic diagram of the feed system of the antenna according to the invention;

Fig. 8 is an illustration of details of construction of the probe member employed with the antenna according to the invention; and

Fig. 9 is an illustration of an alternative coupling arrangement.

Referring to Fig. 1, there is shown an elevation view of an antenna installation according to the invention. I'he antenna as designed for operation at 530 megacycles consists of a galvanized steel tube 20 having a 9% inch inside diameter and an outside diameter of 10% inches, with a half-inch wall. Tube 20 may be made in two lengths, each approximately 20 ft. long,

probes, later to joined by means of flanges at the radiation center of the antenna for ready access to the interior at that point as shown in Fig. l, although it is contemplated that a single length of tubing will be preferred in commercial practice.

The basic radiating system consists'fof four half-wave slots 22 lequally spaced around the circumference of tube 20. There are 22 layers of these half-wave slots, making 88 individual slots in the tube 2i). The slots are driven by radially projecting probes 24 shown in Fig. 2 and more completely described hereinafter.

The antenna is broken into two electrically identical groups of half-wave slots, the slots being spaced approximately one-half wavelength between ends. Each successive layer of slots is preferably rotated 45, with respect to the preceding layer to suppress transmission of the TE1,1 and other non-cylindrical modes within cylinder 26. This construction also inherently provides increased mechanical strength. The modes which do not have cylindrical symmetry would cause unequal excitation of individual slots in a layer resulting in a non-circular horizontal pattern. Other modes need not be suppressed if a dispersed directional pattern is `produced as a result. Horizontal patterns deviating considerably from a circular configuration observed during development work were found to be corrected by staggering the layers. The use of matching be described, also vaids in correcting the eld pattern.

A 31/8 inch outside diameter tube assembly 26 installed within tube 23 acts in conjunction therewith as a transmission ergy to and from the interior of tube and to distribute the energy to slots 22. The cut-olf frequency of the TE1,1 mode in the transmission line thus formed is approximately 550 megacycles.

Tube assembly 26 within the antenna has an inner conductor Ml within the lower half 26B to effect a further transmission line to convey wave energy to the center of the antenna feed system. This is accomplished by dividing conductor 26 into two lengths, 26A and 26B, separated by an insulator 43 which also serves as an end seal for the transmission line formed by inner conductor and conductor 26B. At this point inner conductor 40 is connected to the adjacent end of conductor 26A. troduced or taken from the center of the transmission line formed by conductor 20 and tube assembly 26. Or the structure may be considered as two lengths of transmission line 2li- 26A and 2li-26B connected in series with respect to the feed point. This center feed avoids any vertical pattern tilt or other dissymmetry in vertical pattern with changes in frequency which would be characteristic of end fed broadside arrays. Also, the effect of antenna and tower sway is reduced. The feed point may be shifted off center of the array if desired to produce a phase dif-- ference of the currents in the two halves of the antenna which is accompanied by a corresponding tilt in the vertical pattern. If deemed desirable, this adjustable tilt in vertical pattern may be used to advantage in any particular installation to adjust for particular terrain conditions or cover densely populated valleys, and the like.

Tube assembly 26 is held in place at each end of tube 20 by means of snorting members 30. While these members may be in the form of annular discs and the like, they preferably comprise a collar member 32 split transversely at one point of the circumference to permit clamping,

line to transfer wave 'en- Thus wave lenergy is inand a plurality of spoke members 34 integrally fastened to collar 32. Spokes 34 are a little longer than the distance between the collar 32 and the tube '20 and are crimped as shown at 34a. Spokes 34 are also quite wide in the axial direction of the antenna and relatively thin in the remaining dimension. Due to this construction only ordinary manufacturing tolerances are necessarily observed but an exceedingly strong and well fitting structure is obtained. Bolts 36 are used to fasten members 30 in place and in the tightening process will draw spokes 34 out, .reducing the degree fof crimp 34'a. The drawing out lof -spokes 34 will also tend to spring collar 362 when screw 38 'is loosened, thus facilitating removal of tube assembly 26 Whenever desired. Tube assembly 26 .is fitted with a draw ring 46 having a 'frus'to-'conical base 48 which serves to center 'the tube assembly as it is drawn into or out of tube 2G. The use of spoke members 34 also provides another advantageous feature in that the antenna according to the invention may be prevented from icing and the like by blowing hot air in between tubes 20 and 26 from a heaterblower combination 28 located at the base of tube 20. The circulation of air will also tend to dissipate heat generated in tube 26 due to high current flow and provide free interior ventilation on hot sunny days to prevent excessive interior operating temperature.

Tube assembly 26 is preferably made of copper, and due to the fact that copper and steel have rather widely differing coefcients of expansion, the top shorting member -30 is .not clamped tightly about tube ZSA, but the latter is allowed to expand and contract freely. AA pair of coil spring contact members 39 are employed to `provide electrical contact between collar 32 and tube The length of tube assembly 26 being about forty feet in the described embodiment, it was found vdesira-ble to employ several sets of spacing members 55. Three or four such spacers are used at each of several levels along assembly 26. Referring to Fig. 6, there is shown an example of four spacers 55 adjustably positioned into wall member 20 and held by a collar member 56 locked by a jam nut 51. Each spacer 55 has a nose member 58 of teflon insulating material which prevents damage to tube 26. Nose members 58 are preferably given a high polish so that tube assembly 26 can be readily drawn into and out of the antenna.

Slots 22 are covered by polyethylene slot covers 23. Covers 23 are held in place by end and side clamping fixtures. The convex construction of covers 23 is preferably employed to reduce the area of the slots in which high frequency currents flow. The use of the protruding slot covers 23 also prevents deleterious effects of certain wind velocities on the tube 2B which may setup 'a harmonic vortex wave.

As hereinbefore indicated, 'slots 22 are coupled to 'the interior of the coaxial transmission line formed by conductors 20 and 26 by means of coupling probes 24. The energy introduced therebetween is preferably of the TEM, or transmission line, mode. Each slot 22 has one such probe 24 connected near the center of the slot 'at one edge. If slots 2'2 are spaced center-to-center at an odd multiple of a half-wave apart in the axial direction, the probes 24 are all connected to opposite edges of slots 22. If the slots are spaced center-to-center a multiple of a wavelength in the axial direction, the probes 24 are placed on corresponding edges of the slots.

When one layer only is driven the pattern is closely circular1 and in agreement with theoretical calculations. Energy of modes other than TEM, notably TEi,1, may be present, and steps are taken according to an aspect of the invention to eliminate the effect of these other modes. @ne such step is the 45 staggering of successive slots along the axis of conductor 20. Another step is the use of four matching probes 44. A multiple layer array using a cylinder having a smaller diameter/wavelength ratio than that thus far suggested will give a circular horizontal pattern without staggering successive layers because the TEM and other non-cylindrical modes introduced on the coaxial line within the antenna cylinder by the slot feed probes and matching probes are rapidly attenuated. The upper and lower groups of slots in the present antenna consist of 1l layers each, with a space of about 3 wavelengths between the two groups.

The current passing through the probe capacity also passes through the driving point impedance oi each radiating slot. It was bserved that the system input bandwidth becomes progressively narrower as the number of layers, and consequently the gain, is increased. Therefore, to maintain the original bandwidth, sets or radial matching probes 44 are used between each layer of slots to obtain an impedance bandwidth at the input of each succeeding layer of the antenna which is approximately equal to the bandwidth of the end layers. In some instances two layers of four probes 44 each are used between layers as shown. In other cases one layer will suliice. The vertical location of these probes is not critical. As to horizontal location, it is considered best to place the probes equidistantly between the nearest slots. In the present case that would be 221/2 from each of the nearest slots.

Referring to Fig. 8, there is Shown a detailed drawing of the construction of a probe 24. The outer end is threaded into member 20 and has a frustro-conical bore El and intersecting radial saw slits 53 in the threaded end. A frustro-conical member 62 is drawn into bore 6l by means of a screw 55. The action of screw 65 is to eX- pand the portions of probe 24 between slits 63 against the threaded surface of wall member 23 and thus hold probe 24 rigidly in place. Probes 24 and 44 are similarly constructed.

While shorting members 30 may be adjustably positioned at points permitting a low impedance to be placed across the transmission line sections formed between conductors 26A and 2e, and 25B and 2D, it is obvious that a more rigid construction is desirable. By means of further sets of adjustable tuning probes 54, similar in construction to probes 24 and 44, arranged between the end slots and shorting members 30, the advantages of fixed shorting members are attained without incurring the disadvantages thereof. Probes 54. will be most effective if located a quarter-wavelength from snorting,r members ed. However, the probes are actually placed at a distance less than a quarterwavelength from members 3i! to provide better trimmer action.

Referring to Fig. 7, there is shown a schematic diagram illustrating the electrical operation of the feed system used in the antenna. The tuning and feed probe settings for successive layers usualy diier. The resistor symbols Ri-Rn correspond to the radiation rsistances` of each layer of slots from the outermost ends of the antenna toward the center. The capacity of tuning probes 54 is shown by the symbol C1; that of the matching probes 44 by symbols C2 to C22; and the capacity of the coupling probes 24 by symbols A1 to A11. The probes settings required for matched impedances in the corresponding layers of the top and bottom half of the antenna will usually be different due to small mechanical variations in the antenna structure.

'I'he characteristics of the antenna were determined experimentally. In this determination the antenna was excited as a transmitting antenna but it must be understood that reverse operation as a receiving antenna will be equally efficiently obtained. A matched load was inserted in the end of the antenna tube 29 and the relative magnitude and phase of the voltage across the load was made with one layer of the antenna matched by means of the tuning probes. Various settings of the slot coupling probes gave a curve of additional phase retardation vs. relative power absorbed by the radiating layer. This curve is useful to determine the proper spacing between layers to compensate for the additional phase shift introduced by the tuning probes. The proper amount of power absorbed by each layer of slots relative to that power transmitted to the layers nearer the end was determined for the eleven layers in each of the top and bottom halves of the antenna. The end layers, bottom and top extremity of the complete 22-layer antenna, have no succeeding layers to which power must be transmitted. Consequently, they must utilize or absorb all of the power which is contained in the incident wave. This is accomplished by adjusting the four-slot coupling probes 24 and the shorting member 3l), or the tuning probes 54 at the end of the antenna, until this layer matches the characteristic impedance of the concentric line within the antenna, which is approximately 68 ohms. The second layer from each end must utilize one-half of the power and transmit one-half of the power to the end layers. A combination of settings for coupling probes 24 and tuning probes 44 is then found to provide this power distribution. that is, to reduce the voltage on the matched load in the end of the antenna to 0.707 of the value obtained when no tuning or coupling probes are inserted. The tuning probes 44 must be adjusted for an impedance match each time coupling probes 2li are changed. The setting of the coupling probe for the third layer transmits two-thirds of the incident power and utilizes one-third, the fourth layer utilizes onefourth and transmits three-fourths of the power, and so on, to the eleventh or innermost layer which utilizes one-eleventh of the power and transmits ten-elevenths.

Each layer of the described antenna was adjusted to obtain an impedance match at 530 mc./s. Difliculty in adjustment of the entire antenna by doing each successive layer from each end simultaneously led to the discovery that the tuning probe settings for corresponding layers from each end were not the same if the input impedance was matched. The proper reference conditions on the slotted measuring line for each half of the antenna were obtained by snorting out one-half of the antenna at a point one wavelength from the feed point and substituting a matched load in the unshorted half of the ancessare tensa after all 'feed probes and screws had been removed. The matched -load may be constructed of four radial of phenolic lamisnate about l feet long mounted 'on fa sleeve'of inside `diameter permitting the v'asseriilily to slide freely on conductor 26. The should be fof maximum width ju'st clearing 'the inside srfa'ee of outer steel tube 2'0. The fins are covered on both sides with 377 ohms per square space 'cloth and have a linear taper on the input 'end fabot three wavelengths long. With the load adjusted for a match, the input impedance to the Y'ani'.en'na feeder system will not change when tli'e l'o'ad is movedon conductor '26. 'After the reference 'con ditions are obtained with the matched load, it will be possible to tune each half of 'the antenna either by using the matched load in one half and tuning the other yhalf or `shorting ou't 'the one half with a snorting disc installed an integral number of half waves from the feed point.

While probes 24 have been shown 'and de@ scribed for coupling slots 22 to the interior of the antenna, a loop arrangement may also be used. Such an arrangement is shown in Fig. 9, wherein a loop 42 'of wire is connected across a slot 22 at the edges thereof. The .plane of loop 42 is :in the direction of the longitudinal axis of vslot 22. Such an arrangement Acan vbe poled, .just as were the probes, by reversing the terminals of the loop to the edges of the slots while maintaining the same direction of the winding. The

loops in the upper half` of the antenna `are .poled loppositely to those of the lower half, justas the .probes of one half are on opposite sides of the associated slots, than the probes 'of the other half of the antenna. Coupling loops 42 are 'useful `at low impedance points vwhereas theA probe is use'- ful at high impedance points. Consequently when slots 22 have a length of approximately a wavelength, loops 42 would be preferred to probes 24. The length L of slots vequipped with loops 42 may be three quarters to one and one half wavelengths long. If desired, however, such longer slots 22 can be coupled to the interior of member 2t by using two probes 64 and 64" spaced a half wave apart and located onalternate edges of the slot.

The transmission line Aeiected by conductors 26B and 45 may be extended to the transducer apparatus if desired and may be constructed along known principles of this art'.` However, the commercially available air dielectric con@ centric transmission. line has a uni-form tubular inner conductor with supporting ceramic -d-isc insulators clamped to it at `one-foot intervals. lThis type of line is satisfactory for V. vservice where the characteristic impedance is practically constant. However, the uncompensated beads at periodic intervals make the line behave like a low pass filter with attenuatingbands in the U. H. F, region. The characteristic impedance fluctuates rapidly with frequency and is imaginary over much of the F. band. A line of this type is clearly not suitable for the stringent standing wave requirements of TIV transmitting antenna systems in the U. F. band where a nearly constant resistance load must be used. Therefore, the transmission line employed in practice of the invention was constructed according to 'a method developed by D. W. Peterson, wherein the insulator supports on the transmission line were mounted in undercut spaces on the inner conductor '49. Small series inductances were cut in the faces of the undercut to compensate for the step capacity. The

'the standing' 'wave Ircliaract'e''ristic -oi the .antenna very little, 'when measurements were 'made on the antenna mounted on vthe tower through 200 `ft. of transmission line.

shown 'in Fig. 2, a short transmission line transformer lsection-is employed to 'provide wider band- 'charac'teristics than would otherwise be provided. In one embodiment of the invention two such sections were employed. An alternative' 'construction providing wider band width is that of continuing conductor 4U on into conductive 'tube 26A and connecting the same at a Vabove the lower end of the tube at which the .proper impedance value is obtained.

Thus far the antenna according to thev invention Vhas been described vas having four slots spaced about the periphery of the outer tube `2li. Almost 'any number 'of slots .may be used to good advantage, however. If but one slot is used a eld pattern Aof -cardional shape, similar to that obtained with the .pylon antenna, will result. A bidirectional gure 8 pattern will be produced with two opposing slots. Three or more slots will .provide a circular pattern, the circularity in general being closer to theoretical as the number of slots is increased. An 'antenna with three slots appears to be the best solution when all factors are considered.

The number vof slots in the vertical direction will be determined by the gain and directi-vity required.

The dimensions given above relate only to the description of one model taken as an example, it being understood that obvious modifications in the rarrangement will be suggested to those `skilled -in the art without departing from the 4spirit and scope of the invention. For example, rotation of slots may be at an angle other than 45 to suppress the non-circular modes. Slots 22 need not -be oriented as shown but may be inclined at an angle to the axis of the antenna. Slots 22 may also be of spiral configuration. No coupling probes or loops are needed for the latter arrangements. Skew and spiral slots will Vnot provide horizontal polarization, however. The polarization will be eliptical, circular, etc., depending on the exact coniguration. Couplingl loops for .skew slots will have the .plane of the loop parallel to the axis of the cylindrical members and not the axis of the skewed slot. Also, if a multiple of probes are used the probe lspacing will be a half wavelength ora multiple thereof along the axis of the tubular members.

T-he invention claimed is:

1. An antenna system comprising a conductive tubular member having a number of slots 1ongitudinally arranged therein, said slots each being substantially a half-Wave long at the operating frequency, said number of slots being divided into groups of slots spaced at intervals of a halfwavelength a-t said frequency, there being a plurality of slots in each of said groups of slots equidistantly spaced -about the periphery of said tubular member, a conductor concentrically arranged within said tubular member, each end of said conductor being electrically connected to said tubular member to form a length of concentric transmission line short-circuited at the ends thereof, probe elements connected to said conductive 'tubular member at an edge of each of said slots and .projecting inwardly toward but spaced from said conductor to couple said slots to said concentric transmission line, and means to couple transducer apparatus between said conductor and said hollow conductive tubular memtransmission line in the described installation l7510er.

2. An antenna system comprising a conductive tubular member having a number of slots longitudinally arranged therein, said slots each being substantially a half-wave long at the operating frequency, said number of slots being divided into groups of slots spaced at intervals of a half-wavelength at said frequency, there being a plurality of slots in each of said groups of slots equidistantly spaced about the periphery of said tubular member, a conductor concentrically arranged within said tubular member, each end of said conductor being electrically connected to said tubular member to form a length of concentric transmission line short-circuited at the ends thereof, probe elements connected to said conductive tubular member at an edge of each of said slots and projecting inwardly toward but spaced from said conductor to couple said slots to said concentric transmission line, further probe elements arranged at each end of said tubular member eiTective to adjust the electrical length of said length of concentric transmission line, and means to couple transducer apparatus between said conductor and said hollow conductive tubular member.

3. An antenna system comprising a conductive tubular member having a number of slots longitudinally arranged therein, said slots each being substantially a half-wave long at the operating frequency, said number of slots being divided into groups of slots spaced at intervals of a half-wavelength at said frequency, there being a plurality of slots in each of said groups of slots equidistantly spaced about the periphery of said tubular member, a conductor concentrically arranged within said tubular member, each end of said conductor being electrically connected to said tubular member to form a length 4of concentric transmission line short-circuited at the ends thereof, probe elements connected tc said conductive tubular member at an edge of each of said slots and projecting inwardly toward but spaced from said conductor to couple said slots to said concentric transmission line, further probe elements arranged at each end of said tubular member effective to adjust the electrical length of said length of concentric transmission line, additional probe elements arranged between groups of slots to vary the impedance characteristic along said length of concentric transmission line, and means to couple transducer apparatus between said conductor and said hollow conductive tubular member.

4. An antenna system comprising a tubular conductor having a number of radiant energy transferring slots longitudinally arranged therein, said slots each being substantially a half-wave long at the operating frequency, said number of slots being divided into groups of slots spaced at intervals of a half-wavelength at said frequency, there being a plurality of slots in each of said groups of slots equidistantly spaced about the periphery of said tubular member, a conductive tube assembly concentrically arranged within said tubular member, connections short circuiting each end of said conductive tube assembly to said tubular conductor, coupling elements connected to said tubular conductor at an edge of each of said slots and projecting inwardly toward but spaced from said conductive tube assembly to couple said slots to the space between said conductor and said conductive tube assembly, probe elements arranged at each end of said tubular member intermediate said connections and effective to adjust the electrical length of said tubular conductor and said conductive tube assembly.

5. An antenna system comprising a tubular conductor having a number of slots longitudinally arranged therein, said slots each being substantially a half-wave long at the operating frequency, said number of slots being divided into groups of slots spaced at intervals of a halfwavelength at said frequency, there being a plurality of slots in each of said groups of slots equidistantly spaced about the periphery of said tubularv member, a conductive tube assembly concentrically arranged within said tubular member, supporting members having connections short circuiting each end of said conductive tube assembly to said tubular conductor, said supporting members having at least one aperture therethrough to form a continuous passageway from one end of said antenna to the other between said conductor and said conducting tube assembly, coupling elements connected to said tubular conductor at an edge of each of said slots and projecting inwardly toward but spaced from said conductive tube assembly to couple said slots to the space between said conductor and said conductive tube assembly, probe elements arranged at each end of said tubular member intermediate said connections and effective to adjust the electrical length of said length of concentric transmission line, said conductive tube assembly comprising two elongated conductive elements arranged in end-to-end relationship, one of said conductive elements being hollow, a further conductor within said hollow' conductive element to form a coaxial transmission line therewith and in insulating member interspaced between said conductive elements to constitute an end-sealing member for said coaxial transmission line, said further conductor extending through said insulating member and being connected to the other elongated conductive element, and means to couple transducer apparatus between said further tubular conductor and said hollow conductive element.

6. An antenna system comprising a conductive tubular member having a plurality of groups of slots longitudinally arranged therein, said slots each being substantially a half-wave long at the operating frequency and said groups of slots being spaced at intervals of a half-wavelength at said frequency, the slots of each oi said groups of slots being equidistantly spaced about the periphery of said tubular member, the slots of alternate groups being circumferentially shifted with respect to the slots of the other groups, a conductor concentrically arranged within said tubular member, each end of said conductor being connected to said tubular member, said conductor having an. interruption therein at substantially the center thereof and being hollow for at least the length of one of the portions formed by said interruption, a further conductor arranged in said hollow portion to effect a length of coaxial transmission line, said further conductor being connected to the other portion of said conductor at said interruption, probe elements connected to said conductive tubular member at an edge of each of said slots and projecting inwardly toward but being spaced from said conductor to couple said slots to the concentric transmission line sections eected by said tubular member and said conductor, further probe elements arranged between groups of slots to vary the impedance 1.11' of the concentric transmission line, additional probe elements arranged at each end of said tu bular member to adjust the electrical length ofsaid length of concentric transmission line, and inea-nsY to coupletransducer apparatus between said further conductor-and the hollow portion of' said conductor.

'7'. An antenna systemv comprisingI a conductive tubular member havin-g a number of slots longitudinally arranged therein, said` slots each be ing substantially a half-wave long at the; operating frequency, said number of slots being di-` vided intogroups Vof slots spaced at intervals of a half-wavelength atsaid frequency, their-being four slots in; each of said groups of' slots spaced atninety degree intervals, about the periphery oi" said tubular member, the slots of; alternate groupsV being shifted forty-five degrees about the periphery ofA said' conductive member with respect to the slots ofthe other groups, a conductor concentrically arranged within said tubular member, each end of said conductor beingl connected to said tubular member, said conductor having an interruption therein at substantiallyY the center thereof' and being hollow for at least the length of one of the portions formed by said interruption, a further conductor a1'- rangedinsaid hollow portion to effect alength of coaxial transmission line, said further conductor being connected to the other portion of said conductor at said interruption, coupling probe elements connected to said conductive tubular member at an edge of each of said slots and projecting inwa-rdly impedance matching probe elements arranged between said groups of slots to vary the impedance of said transmission lines, tuning probe elements arrangedat each end of said tubular member effective to adjust the electricalA length oi said length or concentric transmission line and means to couple transducerapeparatus between said further conductor and. the hollow portion ofsadconductor;

S. An antenna structure including an elongated tubular conductor having radiation transferring slots incorporated thereinan elongated cylindrical conductive member having two electrically separate components arranged within said tubular conductor, said tubular conductor and the components ofsaid cylindrical cond-uctive member formingy lengths ofV coaxial transmission line, there beingI conductive radiation coupling elements connectedto-saidtubular conductor and arranged in the space between said conductor and said conductive member to couple said radiation transferring slots to said space, conductive clamping members connected tothe interior of said tubular conductor near the ends thereof and having a portion adapted to tightly engage said cylindrical conductive member to clamp said member in position and to permit insertion and withdrawal of said cylindrical con-l ductive member into and' from said tubular conductor without, affecting said radiation coupling elements, said conductive clamping elements being connected to said tubular conductor by crimped members ofAv conducting material.

9. An antenna structure including an elongated tubular conductor having radiation transferring slot elements incorporated therein, an elongated cylindrical conductive member having two electrically separate components arranged within said tubular conductor,I said tubular conductor and the components of said cylindrical conductive member forming lengths of coaxial transmission line, there being adjustable cou- 12 pling elements conductiviely.l connected to, said tubular conductor and projecting into, the. space between said tubular conductor and saidv con duetive member to,y couplel said radiation transferring slot: elements' to said space, conductiveclamping members connected to the. interior o= said; tubular conductor near the ends thereof and' having a portion adapted to tightly engage saldi cylindricaly conductive member to selectively clampfsxaud member in position and to permit insertion and withdrawal of said' cylindricali conductive memberV into and fromV said tubular conductor without affecting adjustment of said ra diation coupling elements, said conductive clampf ing elementsbeing connected to said tubular con`- ductor by: crimped members of conducting material, one of said clamping members beingA only loosely clamped to ypermit relative movement between saidftubular-conductor and` said cylindrical conductiveI member, one component of said cy-` lindrical conductive memberbeing hollow, a ture ther conductor within said hollow component forming' a transmission linev therewith, and. an insulator member serving both as an end sealr for said transmission line and to, mechanically couple said components together.

l0. An antenna. system including; a length ol concentric transmission line comprising an, outer conductor and a'. central conductor arranged within said outer conductor, connections shortcircwltins'A said outer and central conductors near the ends thereof, said outer conductor having a plurality of elongated radiant energy transferring slots therein, an interruption in said central e conductor near the' center: thereof.. meansl to couple transducer apparatus near the center of said length of concentric transmission. line: at said, interruption to excite said. transmission line in the TEM mode, and coupling elements connected to. said outer conductorat, the edges; of said, slots and substantially the; mid-pointof each of said slots, said. couplingelementsA projecting inwardly' into` the space between said outer and central conductors but being spaced from. said; centralconducimr.`

11.A An antenna systemy comprisingV a conductive tubular member having a number ofi slots thereinJA said slots each being substantially a multiple including unityV ci a halt-wave length long at; the. operating: frequency, said,v number of slots being divided into groupsv of slots spaced at intervals, there being a.` plurality of slots in each of said groups of slotsv spaced symmetrically about the peripheryI of said. tubular member, the slotsz of alternate groups beingV circumferentially shifted with respect tov the slots of` the other groups, a conductor concentricallyarranged within said tubular member, eachend of said conductor being connected to said tubular member, saidl conductor having an interruption therein. at substantially the center thereof and being hollow for at leastv the length of one ofl thev portions formed by said interruption. a further conductor arranged in saidl hollowv portion to` eiieet a length of coaxial transmission line. said further conductorbeing connected toI the,- other portion of said conductor at said interruption, coupling elementsconnected to said conductive tubular member atan edge ofeach of said slots and, projectmg inwardly, means for varying the impedance ofj said transmission lines, tuning probe elements arranged at each end of said tubular member eiective to adjust the electrical length of. said length of concentric transmissionline. and means to couple transducer apparatus between said 13 14 further conductor and the hollow portion of said Number Name Date conductor. 2,543,468 Riblet Feb. 27, 1951 OWEN ORLANDO FIET. 2,574,433 Clapp Nov. 6, 1951 ROBERT MARION SCUDDER. OTHER REFERENCES References Cited in the le of this patent d Microwave Omndirectional Antenna, by H. J.

UNIIIIED Proc. I. R. E., vol. 35, No. 5, pages 474. 478.

Number Name Date slotted cylinder Antenna (Jordan et el.)

2,408,435 Masn OCU 1- 1946 w pages 9o to s3, Electronics February 1947. 214711515 Brown May 311 1949 Slot Feeders and Slot Aerials (Bailey), pages 2480182 Clapp Aug- 30, 1949 617 te 618, Journal of Institute of EE., vel, 93, 2,496,242 Bradley Jan. 31, 1950 Part 1]:[Ay No. 4

2,505,768 Haller May 2, 1950 

